Product Description

Overview

The ABB REX521 is a high-performance Feeder Protection Relay engineered for medium-voltage distribution networks and large three-phase AC motor drives. It integrates protection, monitoring, control, and measurement functions in a single Intelligent Electronic Device (IED). The relay is adaptable for a wide range of applications, including incoming/outgoing feeders, motor feeders, and transformer backup protection. Multiple hardware versions support conventional CT/VT inputs or modern current and voltage sensors, making it suitable for both legacy and modern substations.

Key Features and Capabilities

• Multi-functional protection for feeders and large AC motors, including short-circuit, overcurrent, earth-fault, and thermal overload protection

• Directional and non-directional protection schemes with three-stage settings

• Start-up supervision, stall protection, and thermal tracking for motor drives

• Power quality monitoring, including total harmonic distortion (THD) and waveform analysis

• Integrated self-diagnostics, condition monitoring, and event/fault recording

• Remote and local circuit-breaker control with multi-shot auto-reclosing

Connectivity and Interface

• Supports Modbus (RTU/ASCII), IEC 60870-5-103, SPA, and LON protocols

• Typical I/O: 9 digital inputs, 4 heavy-duty power outputs, 2 signal outputs, 1 internal fault relay

• LCD display with user-configurable navigation and alarm indicators

• Compact and robust design suitable for harsh environments (-40°C to +70°C)

Technical Specifications

Application Scenarios

• Radial distribution networks with isolated, resonant, or solidly earthed configurations

• Motor protection in circuit breaker-controlled medium and large AC drives

• Backup protection for power transformers and high-voltage line relays

FAQ

Q: Can the REX521 support modern sensor inputs?
A: Yes, specialized versions support current and voltage sensors such as Rogowski coils, in addition to conventional CT/VT inputs.

Q: Is the relay suitable for outdoor or harsh environments?
A: Yes, the unit operates reliably in temperatures from -40°C to +70°C.

Q: Can it integrate with SCADA systems?
A: Yes, it supports multiple industrial protocols including Modbus and IEC 60870-5-103 for seamless substation automation integration.